[Lord Carnifex]

Hmm...

I guess part of the question in my mind is, how big does the Great War have to get before it's great?

My thinking, more-or-less, was that without France as a Great Power, there's no pact between France and Russia that leads France to declare war on Germany after Germany declares war on Russia. And without France, would the U.K. really go it alone against Germany? For the purposes of the end goal here, I assume not*. Now, without France, does Russia declare war on Austria-Hungary? Maybe, maybe not. If they do, they might get steamrollered by Germany which is only fighting a one front war (assuming the Germans don't go after Italy, which seems unlikely). Would that be a war great enough to be a Great War? Maybe.

Otherwise, Russia decides that discretion is the better part of valour, and hangs the Serbs out to dry, and WWI fizzles before it lights off.

About the only thing I think leads to greater Prussian annexation of France after the Franco-Prussian war is if the French, instead of agreeing to an Armstice to end the seige of Paris, choose to fight it out to the bitter end. At which point Germany does pretty much whatever they want with it.

* I can see England, and especially the house of Hannover, deciding they have more in common with Germany than either Russia or a rather denuded France. So they stay out of what they feel is a 'Continental War' that doesn't concern them.